You can replace the contents of a specific document in the repository by using its id. The format of the URl and the parameters that you can use are detailed in the service document.
Here is an example of a URL to update the contents of a specific document in a Content Services on-premise instance:
https://localhost:8080/alfresco/api/-default-/public/cmis/versions/1.1/atom/content?id=824ba7cd-dcee-4908-8917-7b6ac0611c97
The request Content-Type must be of the same mime-type as the target document. In this example, we are updating a plain text document.
Content-Type: text/plain; charset=utf-8
The request body is the new content of the document.
Some updated text.
If the request is successful an HTTP CREATED response (status 201) is returned.